(a) Field of the Invention
The present invention relates to a composition for forming a coating layer and a display device having a coating layer prepared from the same, and particularly, to a composition for forming a coating layer capable of controlling light transmittance and body color, improving mechanical strength and contrast, and providing good antistatic and electromagnetic shielding properties, and a display device having a coating layer prepared from the same.
(b) Description of the Related Art
A display device such as a Cathode Ray Tube (CRT) has a curved panel having a predetermined curvature, which causes the display device to sparkle and be image-distorted on the periphery thereof. Therefore, development of a high quality screen on a curved panel field is limited. In order to alleviate these problems, a flat panel display has been proposed and developed.
The cathode ray tube is a device for displaying images on a screen by emitting electron beams from an electron gun assembly and landing them on red (R), blue (B), or green (G) phosphors coated on the screen through a black matrix with a dot or a stripe shape. FIG. 1 shows a cross-sectional view of the cathode ray tube. The panel 10 of the cathode ray tube is composed of a face panel 12 and a curved lateral wall 14 that extends from the periphery of the face panel 12 toward a funnel 20, and is joined to the funnel 20. The funnel 20 includes a neck 24 which is formed on an end of the funnel 20 opposite the end joined to the panel 12, and an electron gun 22 is disposed in the neck 24 of the funnel 20.
The outer surface of the cathode ray tube 10 is coated with a layer 16 having various functions depending upon the type of panel. Examples of the layer include, but are not limited to, a high contrast layer for decreasing light transmittance, an anti-reflection layer for reducing reflectivity, and an antistatic layer for preventing electrostatics and preventing dust from being attracted to the panel. Recently, as concerns that electromagnetic waves exert a harmful influence upon the human body have increased, electromagnetic waves have been strictly restricted by regulations. Therefore, development of a coating layer for shielding electromagnetic waves and the magnetic field that occurs from the display device have been actively pursued. The material and structure of the layer can be determined by considering conductivity, light transmittance, reflectivity, and so on.
In order to provide a display device with antistatic, anti-reflective, and electromagnetic wave shielding properties, a transparent conductive layer is generally applied on the surface of a panel by coating the surface with a coating liquid containing conductive particulates. The transparent conductive layer is a thin coating layer formed on a glass or a plastic substrate having a high light transmittance.
Generally, it is prepared by wet-coating the substrate surface with a composition comprising transparent conductive particles such as a metallic oxide, for example, a tin oxide doped with antimony (Sb) or an indium oxide doped with tin (Sn), and then calcinating it at a low temperature. The wet-coating process includes spin coating, spray coating, or dip coating techniques.
The transparent conductive layer prepared with the above method has a surface resistance of about 107 Ω/□, which is in excess of the surface resistance range of between 102 Ω/□ and 104 Ω/□, and which is required for shielding the electromagnetic waves. In order to decrease the surface resistance to the desired range, the thickness of the conductive layer needs to be increased, a thicker conductive layer degenerates the reflection-reducing effects of the layer. Therefore, it is difficult to provide a transparent conductive layer having low surface resistance as well as good electromagnetic wave shielding and anti-reflection properties by just coating the panel with the tin oxide doped with antimony (Sb) or the indium oxide doped with tin (Sn). Specifically, since a flat monitor is applied with a high level of voltage and has a transparent panel, it is further necessary to provide a transparent conductive layer having a high conductivity and a low light transmittance to meet the regulations on electromagnetic waves set by TCO standard. The TCO standard is a standard conforming to measurement standard MPR-II for a VDU (Visual Display Unit) which is set by SWEDAC (Swedish board for technical accreditation).
One approach to satisfy these requirements is Korean Patent Laid-open Publication No. 2000-50674, which discloses a method for forming a conductive thin layer comprising the step of coating a substrate with a metal colloid dispersed with a single type of metal particle such as Au, Ag, Pd, Ru, Rh, and Pt, or an alloy thereof, in a solvent. Korean Patent Laid-open Publication No. 1999-11487 discloses an antistatic mono-layer prepared by using a composition comprising a metal particulate, a binder, and a solvent. In this method, the surface of the metal particulate is treated with a binder such as polyvinyl alcohol, polyvinyl pyrrolidone, or an oligomer of silicon alkoxide to improve the dispersing state of metal particulates.
It is, however, difficult to save manufacturing costs due to the expense of the metal used for the conductive oxide particulate. Further, since the colloid has a poor coating property and low stability, the coating layer prepared from the colloid tends to be stained and be susceptible to problems in the process so that productivity is decreased compared to the conventional oxide particulate. In spite of the above-mentioned problems, metal colloids are applied as a coating layer to the outer surface of monitors to satisfy the regulations on the electromagnetic waves set by the TCO standard, and accordingly, a need exists for a composition for forming a coating layer suitable for applying to a flat monitor panel.